[CCCL] 瘦身 + 补全: 移除 cudax/python/libcudacxx-tests 冗余文件, 新增 c2h 测试助手 + cmake 构建系统 + 8 个 CUDA thrust examples

变更摘要:
- 删除: cudax/ (783 files, 7.2M) — 实验性组件，竞赛不需要
- 删除: python/ (226 files, 2.0M) — Python 绑定，竞赛不需要
- 删除: libcudacxx/{test,benchmarks,codegen,cmake,share} (4432 files, 31M)
  保留: libcudacxx/include/ (1463 headers, cuda::std 编译依赖)
- 新增: c2h/ (27 files) — CUB Catch2 测试辅助头文件，编译 243 个测试必需
- 新增: cmake/ (29 files) — CCCL 原生 CMake 构建系统
- 新增: thrust/examples/cuda/ (7 files) + cpp_integration/ (1 file)
  async_reduce, custom_temporary_allocation, explicit_cuda_stream,
  global_device_vector, range_view, unwrap_pointer, wrap_pointer, device

结果: cccl_upstream 从 74M→35M (瘦身 53%), 核心内容 100% 保留:
  27/27 tuning headers, 78 benchmarks, 243 tests,
  60 thrust examples, 18 CUB examples, 全部编译头文件

cccl_upstream/cudax/examples/stf/logical_gates_composition.cu

@@ -1,73 +0,0 @@
-//===----------------------------------------------------------------------===//
-//
-// Part of CUDASTF in CUDA C++ Core Libraries,
-// under the Apache License v2.0 with LLVM Exceptions.
-// See https://llvm.org/LICENSE.txt for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-// SPDX-FileCopyrightText: Copyright (c) 2022-2024 NVIDIA CORPORATION & AFFILIATES.
-//
-//===----------------------------------------------------------------------===//
-
-/**
- * @file
- * @brief Composition of boolean operations applied on logical data
- */
-
-#include <cuda/experimental/stf.cuh>
-
-using namespace cuda::experimental::stf;
-
-// z = AND(x,y)
-logical_data<slice<int>> AND(context& ctx, logical_data<slice<int>> x, logical_data<slice<int>> y)
-{
-  assert(x.shape().size() == y.shape().size());
-
-  auto z = ctx.logical_data(x.shape());
-
-  std::string symbol = "(" + x.get_symbol() + " & " + y.get_symbol() + ")";
-  z.set_symbol(symbol);
-
-  ctx.parallel_for(z.shape(), x.read(), y.read(), z.write()).set_symbol("AND")->*
-    [] __device__(size_t i, auto dx, auto dy, auto dz) {
-      dz(i) = dx(i) & dy(i);
-    };
-
-  return z;
-}
-
-// y = NOT(x)
-logical_data<slice<int>> NOT(context& ctx, logical_data<slice<int>> x)
-{
-  auto y = ctx.logical_data(x.shape());
-
-  std::string symbol = "( !" + x.get_symbol() + ")";
-  y.set_symbol(symbol);
-
-  ctx.parallel_for(y.shape(), x.read(), y.write()).set_symbol("NOT")->*[] __device__(size_t i, auto dx, auto dy) {
-    dy(i) = ~dx(i);
-  };
-
-  return y;
-}
-
-int main()
-{
-  const size_t n = 12;
-
-  int X[n], Y[n], Z[n];
-
-  context ctx;
-
-  auto lX = ctx.logical_data(X);
-  auto lY = ctx.logical_data(Y);
-  auto lZ = ctx.logical_data(Z);
-
-  lX.set_symbol("X");
-  lY.set_symbol("Y");
-  lZ.set_symbol("Z");
-
-  auto lB = AND(ctx, AND(ctx, lX, lY), AND(ctx, lX, lZ));
-  auto lC = AND(ctx, NOT(ctx, AND(ctx, lB, NOT(ctx, lY))), lX);
-
-  ctx.finalize();
-}